The present invention relates generally to the field of medical devices, and, more specifically, to electronic leads for implants and tools for using such electronic leads.
Electronic implant devices are used in the medical profession to monitor health processes, such as glucose levels and heart activity, and to control or stimulate health processes, such as controlling heart rate and stimulating muscle function. Examples of implant devices include glucose sensors, pacemakers, muscle stimulators, and the like.
Implanted systems may include multiple devices connected for communication. In this case, a mechanism for electrical transmission between these devices is needed, whether for communication of data, power or both. Typically, due to power and size constraints, electrical transmission is relegated to a single pair of conductors. Two conductors are typically sufficient to send ground and supply voltages from a power supply to an implant device, or, for communication of data between two or more devices.
Because implantable leads are designed to be implanted in the subcutaneous tissue of a patient""s body, the dimensions of such leads can have an impact on the level of comfort of the implant patient and the external appearance of the implant path. Also, the path of the lead implant may be substantially determined by the other devices within the implanted system, limiting options for selecting a least offensive implant path. Typically, a lead of relatively small dimensions and, in particular, a relatively small diameter dimension, will minimize patient discomfort and noticeable protrusions along the implant path. Accordingly, there is a demand in the industry for minimizing the diameter dimension of implantable electronic leads, particularly in sensor applications where, for example, the size of a glucose sensor is of the same order as the diameter of the electrical lead.
Small devices like the glucose sensor may be implemented with no power source of their own, and rely on power extracted from the data signal itself. As power levels are typically low to begin with, it is important that the electrical lead have a high conductivity value to minimize power attenuation over the length of the lead. The lead should also be sufficiently strong and flexible to resist breaking due to any stresses placed on the lead by the insertion process during the implant operation, as well as stresses caused by movement or pressure of the patient""s body during normal activities. Unfortunately, the need for strength, flexibility and high conductivity often limits how small the diameter of an electrical lead can be made.
Other problems with implantable leads concern the connectors used to couple the leads to the implanted devices. For example, most connector structures are of greater diameter than the lead itself. This can cause extra trauma during insertion as these nonuniform structures catch and tear in the body tissues. Further concerns are with the integrity of the connections achieved by the connectors. It is important that the connectors not become disconnected during use. Connection integrity is typically ensured by complicated cam structures or external screws which the surgeon must manipulate during the implant process to lock the connection. Also, fluids and other matter from the exterior implant environment can penetrate the connectors, resulting in a short between conductors. Pacemaker leads have used a single rubber O-ring to seal out fluids. However, there is a need for connectors that can provide a more efficient seal to inhibit such short circuits from occurring.
Finally, the junction between the cable and the connectors is often placed under greater amounts of stress than other portions of the lead. Therefore, the lead is more likely to fail at that point. Pacemaker leads have tried to overcome this weakness in the cable by molding large ball-like or disk-like rubber structures around the lead at those points to resist excessive flexure. Such external structures only serve to widen the diameter of the cable at those points, generate unwanted protrusions, and complicate insertion procedures.
Thus, there remains a demand in the industry for new and improved electrical lead structures that have reduced diameter dimensions, yet which do not compromise other operational characteristics, such as the strength to resist stress and the conductivity to minimize attenuation. Further, lead structures are needed that minimize diameter-related anomalies caused by connectors and stress relieving structures, and that provide secure connections without requiring complicated manipulations by a surgeon during insertion.
Embodiment of the present invention relate generally to implant devices having one or more lead cables for the transmission and/or reception of electrical signals between two or more electronic devices in a medical implant environment. Particular embodiments relate to cables, connectors and tools for such devices and methods of making and using the same, which address one or more of the concerns and demands in the industry as noted above.
Embodiments of the invention may employ cable structures that reduce the diameter and improve the strength of the lead, as compared to prior cable technologies. In this manner, smaller leads may be used in implant procedures to reduce the initial physical trauma of the implant procedure, and the continuing discomfort and physical trauma caused by the constant presence of the implanted lead, without compromising the strength and conductivity of the lead. Embodiments of the invention may also employ connector structures that simplify the operation and enhance the reliability of the lead connectors, as compared to prior connector configurations. Thus, implant leads may be connected quickly and easily, without sacrificing retention strength, circuit integrity or the surgeon""s confidence that a connection was made. Further, embodiments of the invention may also employ insertion tools to minimize surgical trauma and maximize surgical efficiency, as compared to prior implant procedures. In this manner, leads may be implanted quickly and easily, without sacrificing safety. Various preferred embodiments may be particularly suited for implant environments. Other preferred embodiments may be employed in external (non-implant) environments.
A sensor lead according to an embodiment of the invention includes a coaxial cable structure, a female connector and a male connector. The cable structure includes an outer insulator tube containing an inner coil and an outer coil separated by an inner insulator tube. The inner and outer coils may be helical ribbon conductors that each represent a separate electrical channel. In some embodiments, the helical ribbon conductors include multiple adjacent wires configured in a ribbon strip that is twisted about a central axis. In this manner, a strong and conductive cable is formed that is also both thin and flexible. In some embodiments, each wire is made up of a highly conductive silver core surrounded by a durable cobalt alloy. According to one aspect of the invention, a tolerance value may be determined for maximum radial offsets by any one wire in a coil, to prevent stress points along the cable. Further, a nominal coil spacing distance may be determined to provide a desired balance of strength and flexibility.
A female connector according to an embodiment of the invention has a female connector body including two conductive body members separated by a middle insulator. The female connector body defines an inner cavity configured to accept a male connector via insertion. Within grooves along the interior walls of the connector body, the connector includes the following: respective conductive tension members electrically coupled to each of the conductive body members, and a seal molded into the middle insulator to electrically isolate the interiors of the conductive body members from each other. In some embodiments, the conductive tension members are implemented by toroidal springs oriented to apply radially directed tension onto respective conducting elements of the male connector for electrical conduction, as well as connection retention. Wear-resistant members may be used to prevent the conductive tension members from damaging the middle insulator. According to one aspect of the invention, the middle insulator may be formed of a resilient material, such as polysulfone. The middle insulator may then be coupled to each of the conductive body members using a friction fit, obviating any need for adhesives.
According to another aspect of the invention, the seal in the middle insulator is configured with an umbrella-shaped ridge for engaging a similar ridge on the male connector. In addition to providing a seal and additional retention force, the umbrella-shaped ridge may provide tactile feedback to a surgeon when the male and female connectors are firmly engaged, improving confidence in the connection. In a further aspect of the invention, a second seal may be provided near the mouth of the female connector body to engage the male connector and isolate the interior of the female connector from the outer implant environment, improving reliability of the connection. In some embodiments, the combined retention force of the conductive tension members and the intervening seals are sufficient to obviate any need for more complex retention mechanisms, allowing a simple unidirectional insertion process.
In yet a further aspect of the invention, the cable maintains a uniform diameter, but for where the cable joins the female connector. At this junction, the outer conducting coil wraps around the exterior of the female connector body to be electrically coupled to the exterior surface of one of the conducting body members. The female connector and the outer coil may then be overmolded with a protective insulating material. In some embodiments, suture holes or rings may be added to the female connector during the overmolding process.
A male connector according to an embodiment of the invention includes a conductive surface and a conductive pin configured to engage respective tension members of the female connector. An insulating member may be formed between the conductive surface and the conductive pin, and provides, in some embodiments, a ridge configured to engage the umbrella-shaped ridge of the female connector. In further preferred embodiments, the male connector is configured to have a diameter no greater than that of the lead cable.
In further embodiments of the invention, a flexible braided cylinder is used as a strengthening apparatus where the lead cable and the male connector are joined. During an overmolding process for the male connector, the braided cylinder is infused with molding material, such as silicon rubber, until the braided cylinder is generally the same diameter as the cable.
A lead implant process according to an embodiment of the invention utilizes an insertion tool to tunnel a desired lead path through the subcutaneous tissue of a patient. The insertion tool includes a rigid, elongated member with a hollow bore and a detachable bullet-shaped member or endpiece. A rod, having a connector member on one end, is configured to slide through the bore of the elongated member for purposes of connecting to the lead and drawing the lead into the elongated member.
In practice, according to one embodiment, a surgeon inserts the elongated member into a patient, for example, through a source incision near a first implant device. The elongated member is then guided through the subcutaneous tissue of the patient until the detachable bullet-shaped member exits a destination incision near a second implant device. The detachable member is removed to expose the connector member of the rod, and the lead is attached to the connector member. The surgeon may then draw the lead into the elongated member by pulling the rod through the hollow bore. Once the connector member is outside the bore, the lead is detached and the elongated member is removed from the patient, leaving the lead in place within the lead path formed by the insertion tool. The lead may then be connected to the implant devices and sutured in position.
Embodiments of the invention may employ any one or combination of aspects described herein for minimizing or reducing the required diameter of the cable structure, simplifying the operation and enhancing the reliability of the lead connectors, minimizing surgical trauma and maximizing surgical efficiency. In one preferred embodiment, all aspects described herein may be employed to result in a lead structure that is small, strong, reliable and easy to use.
These and other aspects and advantages of the invention will be apparent to one of skill in the art from the accompanying detailed description and drawings. Each of the above-noted aspects of the invention, as well as other aspects of the invention, may be practiced separately or in various combinations.